The present invention is directed generally to snap action valves and more specifically to such valves which are specifically adapted for use to control flow of fluids in response to a control signal such as may be used in gas fired appliances or the like.
Snap action valves of the type with which the present invention is concerned typically employ a valve member supported on one end of a snap blade, the other end of which is fixedly supported on the housing. A bimetallic actuator is utilized to effect movement of the free end of the snap blade so as to move the valve member into and out of sealing engagement with a valve seat surrounding a discharge passage.
The bimetallic actuator may include a first bimetallic active blade, one end of which is fixedly supported on the housing and having an electrically actuated heating coil provided thereon. A bimetallic compensator blade may be secured to the free end of the active blade and is operatively interconnected to the snap blade adjacent the valve carrying end by an over-center spring. When in a closed position, the spring acts between the compensator blade and the snap blade to augment the closing force exerted on the valve member by the snap blade. When the valve is actuated to an open position, the compensator blade is moved through an opening in the snap blade as a result of heating of the active blade by the heating coil thereby initially compressing the spring and causing its line of action to pivot about the snap blade until its line of action causes the snap blade to move the valve member out of engagement with the valve seat in a xe2x80x9csnapxe2x80x9d like movement.
The use of snap action type valve opening arrangement ensures that the valve is opened fully as quickly as possible and in order to assist in this rapid opening, it is desirable that the xe2x80x9chinge pointxe2x80x9d or area of flexing of the snap blade be located away from the end on which the valve is mounted. However, the opening in the snap blade provided to accommodate movement of the bimetallic actuator results in an area of reduced stiffness thus shifting the xe2x80x9chinge pointxe2x80x9d into relatively close proximity to the valve member.
The present invention overcomes this problem by incorporating stiffening ribs on the snap blade extending from a location adjacent the valve member along the area in which the opening is located. These stiffening ribs serve to increase the rigidity of the snap blade in the area of the opening and thus shift the hinge point away from the spring connection and valve member. In addition the present invention may incorporate a rib extending substantially diametrically with respect to the opening in the snap blade within which the valve member is supported and also extending substantially perpendicular to the longitudinal axis of the snap blade. This rib serves to provide a generally line contact with the valve member so as to enable it to pivot thereabout as the valve member moves into engagement with the valve seat. This pivoting movement enables the valve member to accommodate relative angulation between the plane of the valve carrying end of the snap blade and the valve seat as the member moves into engagement therewith.
As previously mentioned, the bimetallic actuator incorporates an active bimetallic blade and a compensator bimetallic blade connected to the free end of the active blade. While the active blade (containing the heating coil) deflects in response to heating thereof to open the valve, the compensator blade is provided in order to compensate for deflection of the active blade as a result of changes in the ambient temperature. However, because of the interconnection between the compensator blade and active blade, some of the heat being applied to the active blade by the heating coil will be conducted to the compensator blade resulting in undesirable offsetting deflection thereof.
In one embodiment, the present invention provides one or more longitudinally extending reinforcing ribs on the compensator blade extending from its point of attachment to the active blade toward the free end thereof. These stiffening ribs will serve to resist deflection of the compensator blade in the area adjacent its connection with the active blade which will be the area experiencing the greatest heating from the active blade. Thus in this manner the effect of heat conduction from the active blade to the compensator blade will be reduced or minimized.
In another embodiment, the compensator blade is secured to the snap blade and the only interconnection with the active blade is via the spring. This arrangement effectively eliminates the conductive heat transfer from the active blade to the snap blade.
It is desirable to insulate the active blade from the current flowing through the heater coil and to minimize the time and effort required to assemble the heater wire to the active blade.
In the present invention, the active blade is provided with an opening through which the heater strip is passed. Thereafter, two ends of the heater strip or tape are wrapped about the active blade together along the length of the active blade. The free ends of the heater tape may then be suitably secured to electrical contacts provided on the housing.
In another embodiment the snap blade is provided with recesses or cutouts adjacent its secured end which serve to increase the flexibility of the snap blade in the area closely adjacent its point of securement. Also an arcuate rib may be provided at the free end of the snap blade to resist possible deflection in the area in which the valve member is supported.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.